CMake/sql find modules: read foo_ROOT env var if available

Even though we set foo_ROOT in the provisioning scripts and CMake is
picking it up as the base dir, we should also use it as CMake variable
so we can look in other directories below foo_ROOT.

Pick-to: 6.8
Change-Id: I193d8ff1c216a669162569d71891c3eb7b9b030f
Reviewed-by:  Alexey Edelev <alexey.edelev@qt.io>

cmake/FindInterbase.cmake

@@ -21,6 +21,12 @@
 # ``Interbase::Interbase``
 #     The Interbase client library
 
+if(NOT DEFINED Interbase_ROOT)
+    if(DEFINED ENV{Interbase_ROOT})
+        set(Interbase_ROOT "$ENV{Interbase_ROOT}")
+    endif()
+endif()
+
 find_path(Interbase_INCLUDE_DIR
           NAMES ibase.h
           HINTS "${Interbase_INCLUDEDIR}" "${Interbase_ROOT}/include"

cmake/FindMySQL.cmake

@@ -40,7 +40,11 @@
 #     The mysql client library
 
 if(NOT DEFINED MySQL_ROOT)
-    find_package(PkgConfig QUIET)
+    if(DEFINED ENV{MySQL_ROOT})
+        set(MySQL_ROOT "$ENV{MySQL_ROOT}")
+    else()
+        find_package(PkgConfig QUIET)
+    endif()
 endif()
 if(PkgConfig_FOUND AND NOT DEFINED MySQL_ROOT)
     pkg_check_modules(PC_MySQL QUIET "mysqlclient")

cmake/FindOracle.cmake

@@ -21,6 +21,12 @@
 # ``Oracle::Oracle``
 #     The oracle instant client library
 
+if(NOT DEFINED Oracle_ROOT)
+    if(DEFINED ENV{Oracle_ROOT})
+        set(Oracle_ROOT "$ENV{Oracle_ROOT}")
+    endif()
+endif()
+
 find_path(Oracle_INCLUDE_DIR
   NAMES oci.h
   HINTS ${Oracle_INCLUDE_DIR} "${Oracle_ROOT}" "${Oracle_ROOT}/include" "${Oracle_ROOT}/sdk/include"